Non-isothermal and isothermal cold crystallization of glass-forming chiral smectic liquid crystal (S)-4′-(1-methyloctyloxycarbonyl) biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluorobutoxy) heptyl-1-oxy]-benzoate

Abstract

The mesomorphic behaviour as well as the kinetics of the isothermal and non-isothermal cold crystallization of the liquid-like smectic SmCA⁎ phase in (S)-4′-(1-methyloctyloxycarbonyl) biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluorobutoxy) heptyl-1-oxy]-benzoate (3F7HPhH7) were studied using differential scanning calorimetry, polarized optical microscopy and Fourier transform infrared spectroscopy supported by quantum chemical DFT calculations. The process of cold crystallization under isothermal conditions was treated in terms of Avrami and Avrami-Avramow models, and under non-isothermal conditions it was described by Ozawa, Mo, Kissinger and Augis-Bennett models. Non-isothermal cold crystallization of the 3F7HPhH7 compound was achieved by two different mechanisms: one depending on diffusion rates (for slow heating) and second one based on the nucleation process (for fast heating). The activation energy of non-isothermal cold crystallization was found equal to 130 and 50 kJ/mol for slow and fast heating, respectively. Cold crystallization under isothermal conditions depends primarily on diffusion rates with the activation energy equalled 133 kJ/mol. The obtained values of the Avrami exponent nA and the Ozawa exponent nO suggest that the crystal growth is three-dimensional.